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  Copyright (c) 2015-2018 Jean-Marc VIGLINO,
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  <title>ol-ext: style chart</title>
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  <meta name="description" content="ol.style.Chart is an image style to draw statistical graphics (bar or pie charts) on a map." />
  <meta name="keywords" content="ol3, style, vector, statistic, chart, pie, animation" />

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  <a href="https://github.com/Viglino/ol-ext" class="icss-github-corner"><i></i></a>

  <a href="../../index.html">
    <h1>ol-ext: chart style + values</h1>
  </a>
  <p class="info">
    The <i>ol.style.Chart</i> is an image style to draw statistical graphics (bar or pie charts) on a map.
    <br/>
    This example show how to display values on a pie chart using a style function.
  </p>

  <!-- DIV pour la carte -->
  <div id="map" style="width:600px; height:400px;"></div>
  <div class="options">
    Select a feature to show its values.
  </div>
  
  <script type="text/javascript">
  // Layers
  var layer = new ol.layer.Geoportail({ layer: 'GEOGRAPHICALGRIDSYSTEMS.PLANIGNV2' });
    
  // The map
  var map = new ol.Map({
    target: 'map',
    view: new ol.View({
      zoom: 6,
      center: [166326, 5992663]
    }),
    layers: [layer]
  });

  // Style function
  var styleCache={};
  
  function getFeatureStyle (feature, sel) {
    var k = $("#graph").val()+"-"+ $("#color").val()+"-"+(sel?"1-":"")+feature.get("data");
    var style = styleCache[k];
    if (!style) {
      var radius = 15;
      // area proportional to data size: s=PI*r^2
      radius = 8* Math.sqrt (feature.get("sum") / Math.PI);
      var data = feature.get("data");
      radius *= (sel?1.2:1);
      // Create chart style
      style = [ new ol.style.Style({
        image: new ol.style.Chart({
          type: "pie", 
          radius: radius, 
          data: data, 
          rotateWithView: true,
          stroke: new ol.style.Stroke({
            color: "#fff",
            width: 2
          }),
        }),
        zIndex: sel ? 1 : 0
      })];

      // Show values on select
      if (sel) {
        var sum = feature.get("sum");
      
        var s = 0;
        for (var i=0; i<data.length; i++) {
          var d = data[i];
          var a = (2*s+d)/sum * Math.PI - Math.PI/2; 
          var v = Math.round(d/sum*1000);
          if (v>0) {
            style.push(new ol.style.Style({
              text: new ol.style.Text({
                text: (v/10)+"%", /* d.toString() */
                offsetX: Math.cos(a)*(radius+3),
                offsetY: Math.sin(a)*(radius+3),
                textAlign: (a < Math.PI/2 ? "left":"right"),
                textBaseline: "middle",
                stroke: new ol.style.Stroke({ color:"#fff", width:2.5 }),
                fill: new ol.style.Fill({color:"#333"})
              })
            }));
          }
          s += d;
        }
      }
    }
    styleCache[k] = style;
    return style;
  }

  // 30 random features with data: array of 4 values
  var ext = map.getView().calculateExtent(map.getSize());
  var features=[];
  for (var i=0; i<30; ++i){
    var n, nb=0, data=[];
    for (var k=0; k<4; k++) {
      n = Math.round(8*Math.random());
      data.push(n);
      nb += n;
    }
    features[i] = new ol.Feature({
      geometry: new ol.geom.Point([ext[0]+(ext[2]-ext[0])*Math.random(), ext[1]+(ext[3]-ext[1])*Math.random()]),
      data: data,
      sum: nb
    });
  }
  var vector = new ol.layer.Vector({
    name: 'Vecteur',
    source: new ol.source.Vector({ features: features }),
    // y ordering
    renderOrder: ol.ordering.yOrdering(),
    style: function(f) { return getFeatureStyle(f); }
  })

  map.addLayer(vector);

  // Control Select 
  var select = new ol.interaction.Select({
    style: function(f) { return getFeatureStyle(f, true); }
  });
  map.addInteraction(select);

  </script>
  
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